1. Field of the Invention
The present invention relates to a work, or workpiece, clamping apparatus for clamping a work by a pair of fingers.
2. Description of the Related Arts
A work clamping apparatus has been known in which a work is clamped by a pair of fingers. In general, this type of clamping apparatus employs a sensing system incorporating a sensor such as a limit switch, an optical fiber, a proximity switch or the like capable of sensing the state of clamping of the work.
A problem, however, is encountered when this type of sensing system is applied to general-purpose fingers such as those mounted on an NC machine. Such general-purpose fingers are broadly used since they ar designed to be adaptable to a variety of types of works or parts. Since these fingers engage with various works in a variety of postures and positions, sensing of the state of the clamp may fail according to the position of the clamp.
More specifically, when a cylindrical first work b is clamped by fingers a as shown in FIG. 1A, state of clamp can be sensed through a sensor c regardless of the size of the cylindrical work b because the sensor c always opposes a part of the cylindrical work b. However, when a second work d having a stepped portion is clamped by the fingers a as shown in FIG. 1B, no portion of the work d opposes the sensor c, so that the sensor cannot sense the state of the clamp. In consequence, another set of clamping fingers with a sensor specifically set for the detection of the work d has to be used. Thus, the use of general-purpose fingers, which inherently have wide adaptability to a variety of types of works, is undesirably limited due to difficulty in sensing such a variety of types of works.